U.S. patent number 4,203,784 [Application Number 05/902,811] was granted by the patent office on 1980-05-20 for grain oriented electromagnetic steel sheet.
This patent grant is currently assigned to Nippon Steel Corporation. Invention is credited to Katsuro Kuroki, Osamu Tanaka.
United States Patent |
4,203,784 |
Kuroki , et al. |
May 20, 1980 |
Grain oriented electromagnetic steel sheet
Abstract
A grain oriented electromagnetic steel sheet has a plurality of
linear fine strains having a traverse section of a concave hollow
on it in the steel sheet shows a very low iron loss in its use.
Inventors: |
Kuroki; Katsuro (Kitakyushu,
JP), Tanaka; Osamu (Nohgata, JP) |
Assignee: |
Nippon Steel Corporation
(Tokyo, JP)
|
Family
ID: |
12865293 |
Appl.
No.: |
05/902,811 |
Filed: |
May 4, 1978 |
Foreign Application Priority Data
|
|
|
|
|
May 4, 1977 [JP] |
|
|
52-50667 |
|
Current U.S.
Class: |
148/111;
148/308 |
Current CPC
Class: |
H01F
1/14783 (20130101); C21D 8/1294 (20130101) |
Current International
Class: |
C21D
8/12 (20060101); H01F 1/12 (20060101); H01F
1/147 (20060101); H01F 001/04 () |
Field of
Search: |
;148/111,31.55,31.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rutledge; L. Dewayne
Assistant Examiner: Sheehan; John P.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Claims
We claim:
1. A method of treating a grain oriented steel to improve the iron
loss which comprises treating a grain oriented electromagnetic
steel sheet containing a glassy film formed by an annealing
separator on the surface thereof and which sheet has been subjected
to a finished annealing operation by imparting a plurality of
linear strains to the base steel sheet through the glassy film by
forcefully moving a rotatable body over the glassy film, said
linear fine strains being formed at an angle of 45.degree. or more
to be the rolling direction of the steel sheet said linear strain
having a depth of 5 .mu.m or less, a width of 600 .mu.m or less and
wherein the distance between adjacent strains is 2.5 to 15 mm.
2. A method according to claim 1 in which a secondary coating is
formed over said glassy film and the rotatable body is forcefully
moved over the secondary coating to impart the linear fine strains
to the base steel sheet through the coatings, said secondary
coating being selected from the group consisting of compounds of
phosphoric acid, organic compounds and an ultraviolet ray-hardening
resin to improve the insulation of the steel sheet.
3. A method according to claim 1, wherein the rotatable body is a
spherical roller having a convex contact surface.
4. A method according to claim 1 in which the direction of the
strains to be imparted is substantially traverse to the rolling
direction.
5. A method according to claim 1 in which the excitation
characteristics (B8) of the base steel sheet subjected to the
finishing annealing is 1.90 or more.
6. A method according to claim 11 wherein the distance between
adjacent strains is 2.5 to 10 mm.
7. A grain oriented magnetic steel sheet having a glassy film on
the surface thereof, which steel sheet has been subjected to a
finishing annealing, said steel sheet containing silicon in an
amount of 4.0% or less and being characterized in that it contains
a plurality of strains imparted through the glassy film by a
rotatable body, in which the strains have a depth of 5 .mu.m or
less, a width of 600 .mu.m or less and the distance between the
adjacent strains being 2.5 to 15 mm and wherein the direction of
the fine strains is at an angle of 30.degree. or more to the
rolling direction of the steel.
8. A grain oriented electromagnetic steel sheet according to claim
7 in which the direction of the strain is traverse to the rolling
direction.
9. A grain oriented electromagnetic steel sheet according to claim
7 in which the excitation characteristics (B8) of the base steel
sheet subjected to the final annealing is 1.90 or more.
10. A grain oriented electromagnetic steel sheet according to claim
7 in which the base steel sheet has a further coating consisting
essentially of one member of the group consisting of compounds of
phosphoric acid system, compounds of organic system and a
ultraviolet ray hardening resin on the film.
11. A grain oriented electromagnetic steel sheet according to claim
7 in which the direction of the fine strains is 45.degree. or more
to the rolling direction of the steel sheet.
12. A steel sheet according to claim 7, wherein the distance
between adjacent strains is 2.5 to 10 mm.
Description
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to a grain oriented electromagnetic steel
sheet having linear fine deformed portions which are hereinafter
referred to as fine strains or linear strains and having a very low
iron loss. The grain oriented electromagnetic steel sheet is a
crystal-oriented steel sheet wherein most of the crystal grains are
magnetically accumulated in ideal directions. Such a steel sheet is
in general classified into two kinds of steel sheets i.e. a grain
oriented steel sheet and a double oriented steel sheet. When they
are represented by Miller indices, the former consists of the
crystal grains having (110) surface in parallel with the surface of
the steel sheet and easily magnetizable axis [100] in parallel with
the rolling direction and the latter consists of the crystal grains
having (100) surface in parallel with the surface of the steel
sheet and easily magnetizable axis [100] in parallel with the
rolling direction.
It is preferable to apply this invention to the grain oriented
electromagnetic steel sheet and, therefore, the following
descriptions are directed to the grain oriented silicon steel
sheet, the ideal directions of which are represented by (100) and
[001]. Of course, the "electromagnetic steel sheet" and the
"silicon steel sheet" herein have the same meaning.
The excitation characteristics of a steel sheet is improved by
allowing all the crystal grains of the steel sheet to come near
(110) [001] ideal directions and therewith the iron loss thereof is
generally decreased. Therefore, many attempts have been made to
elevate the degree of the accumulation of the above texture. As a
result, the electromagnetic steel sheet showing such a low iron
loss that W17/50 is 1.03 watt/kg or so has nowadays been
manufactured industrially when the thickness of the steel sheet is
0.30 mm. In this connection; the W17/50 means the iron loss in the
magnetic flux density of 1.7 T. In addition, the T is short for
Tesla which is the unit of magnetic flux density (wb/m.sup.2).
It has, however, been gradually made clear that it is difficult to
further decrease the iron loss rapidly by only allowing the crystal
grains to come near the ideal directions. The reason is as
follows:
In general, the iron loss depends upon the size of the crystal
grain as well as the excitation characteristics. The crystal grain
must be coarsened to a certain extent in order to enhance the
excitation characteristics whereby the amount of the decrease in
iron loss is offset.
Therefore, the other means must be employed to further reduce the
iron loss below the lowest level of iron loss at the present time.
The method of giving a steel sheet to a tension is known as one of
the other means. The method of imparting the tension to the steel
sheet by forming an insulating coating thereon has been proposed in
this industrial field. However, there is a limitation in the
tension which can be obtained by the coating and, therefore, there
is also a limitation in the iron loss improved by the impartment of
the tension. As a result of this, the lowest level of the iron loss
obtained by the addition of the effect of the tension has been the
above-mentioned 1.03 W/Kg or so.
There is another method for reducing the iron loss. The feature of
the method is to finish the surface of the steel sheet subjected to
a finishing, or final, annealing to a mirror, or speculum,
condition by a chemical or electrolytic abrasion. The iron loss of
the steel sheet produced by the method depends largely upon the
degree of the smoothness of the surface and, when the steel sheet
is coated with an insulating coating, the iron loss of the steel
sheet is deteriorated.
In addition, another method for decreasing the iron loss is
disclosed in U.S. Pat. No. 3,647,575. The feature of the method is
to provide flaws, or grooves, to the surface of a steel sheet. The
provision of the grooves is carried out by scratching or strongly
rubbing the surface of the steel sheet with a knife, a razor blade
or such a very hard material as emery powder or a steel brush. In
the method the decrease of the iron loss can be expected but when
the steel sheets are piled, or stacked, the space factor, or
stacking factor, is not only deteriorated steeply but also the
strain of the magnetism is increased largely. Furthermore, there is
the fatal disadvantage that, when the steel sheets provided with
the flaws are stacked, or piled, an expected value of the iron loss
can not be obtained. That is, in the steel sheet provided with the
flaws the Epstein value is higher than SST value wherein the SST is
a single sheet measuring apparatus which is hereinafter referred to
as SST.
The reasons are assumed as follows:
In the steel sheet the portions provided with the flaws become
thinner that the other portions and, therefore, a part of the flux
is discharged from the surfaces of the steel sheet. Consequently,
in the SST measurement the decrease of the iron loss is observed
but, when the steel sheets are piled, the flux discharged from one
of the steel sheets piled is received by the above and below steel
sheets adjacent to the one so that the magnetizm element of the
direction vertical to the steel sheet is generated and thereby the
iron loss is deteriorated.
Thus, the providing of the flaws has the fatal disadvantage, in
case that the steel sheets provided with the flaws are employed in
a pile as a core for a transformer or a coiled core. Therefore, the
providing of the flaws has not been applied to any commercial
articles or devices.
It is, therefore, an object of this invention to overcome all the
disadvantages as mentioned above.
It is another object of this invention to provide a grain oriented
electromagnetic steel sheet having a very low iron loss which can
be employed commercially.
It is still another object of this invention to provide a grain
oriented electromagnetic steel sheet provided with fine strains but
without any return strains due to the provision of the fine
strains.
According to this invention, there is provided a grain oriented
electromagnetic steel sheet (1) which comprises a base steel sheet
with an inorganic film or a glassy film subjected to a final
annealing, the steel containing Si in an amount of 4.0% or less,
and a plurality of linear fine strains imparted to the base steel
through the film.
According to this invention, there is also provided a steel sheet
(2) according to the steel sheet (1) in which the strain is given
by a body of rotation.
According to this invention, there is also provided a steel sheet
(3) according to the steel sheets (1) and (2) in which the
direction of the strain is traverse to the rolling direction.
According to this invention, there is also provided a steel sheet
(4) according to the steel sheets (1) to (3) in which the strain
has the depth of 5 .mu.m or less and the width of 600 .mu.m or
less, and the distance between the adjacent two strains is 2.5 to
10 mm.
According to this invention, there is also provided a steel sheet
(5) according to steel sheets (1) to (4) in which the excitation
characteristics (B8) of the base steel sheet is 1.90 or more.
According to this invention, there is also provided a steel sheet
(6) according to the steel sheets (1) to (5) in which the base
steel further has a coating consisting essentially of one member of
the group consisting of compounds of phosphoric acid system,
compounds of organic system and a ultraviolet ray hardening resin
on the film.
According to this invention, there is also provided a steel sheet
(7) according to the steel sheets (1) to (6) in which the direction
of the fine strains is 30.degree. or more to the rolling direction
of the steel sheet.
According to this invention, there is also provided a steel sheet
(8) according to the steel sheet (7) in which the direction of the
fine strain is 45.degree. or more to the rolling direction of the
steel sheet.
According to this invention, there is also provided a steel sheet
(9) according to the steel sheet (1) in which said strain is its
very small amount in the traverse direction.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 (a) is a microphotograph (200 magnifications) of the
sectional view of an electromagnetic steel sheet of this invention
provided with fine strains.
FIG. 1 (b) is a microphotograph (200 magnifications) of the
sectional view of the same electromagnetic steel sheet as that of
FIG. 1 (a) provided with a flaw by the sharp edge of a knife.
FIG. 2 (a) is a microphotograph (100 magnifications) showing the
aspect of the fine strains observed by a transition pit method
after the glassy film of an electromagnetic steel sheet of this
invention with fine strains is peeled off.
FIG. 2 (b) is a microphotograph (100 magnifications) showing the
aspect of the flaw of the same steel sheet as that of FIG. 2 (a)
provided by a knife of fine strains imparted and the rate of
improvement of the L direction of iron loss.
FIG. 2 (c) is an enlarged sectional view of FIG. 2 (a).
FIG. 2 (d) is an enlarged sectional view of FIG. 2 (b).
FIG. 2 (e) is a sectional view showing the case that two steel
sheets of FIG. 2 (c) are stacked.
FIG. 2 (f) is a sectional view showing the case that two steel
sheets of FIG. 2 (d) are stacked.
FIG. 3 is a graph showing the characteristics of the iron loss
before and after the impartment of fine strains.
FIG. 4 (a) is a graph showing the relation between the
direction.
This invention is further described with reference to the
accompanying drawings.
FIG. 4 (b) is a graph showing the relation between the direction of
fine strains imparted and the rate of improvement of the C
direction the iron loss of FIG. 4 (a).
FIGS. 5 (a) and (b) are graphs showing the relation between the
distance, or space, of the impartment of fine strains and the iron
loss.
FIGS. 6 (a), (b) and (c) are graphs showing the relation between
the distance of the impartment and the load weighted for the
impartment of the fine strains.
FIGS. 7 (a) and (b) are graphs showing the relations between the
width of the fine strain and the flux density and between the width
of the fine strain and the iron loss.
FIG. 8 is a graph showing the relation between the B8 before and
after the impartment of the fine strains and W17/50.
FIG. 9 (a) is an oblique view of one example of a preferable
rollers to be employed in this invention.
FIG. 9 (b) is a front view of the roll of FIG. 9 (b).
This invention can be applied to a grain oriented electromagnetic
steel sheet containing Si in an amount of 4.0% or less. If the Si
content in the steel sheet exceeds 4.0%, the cold workability of
the steel sheet is extremely deteriorated whereby it is made
difficult to produce a grain oriented electromagnetic steel sheet
industrially at this technical level.
The first feature of the grain oriented electromagnetic steel sheet
of this invention is that the steel sheet has linear fine strains
(which are hereinafter called liner strains or fine strains)
provided thereon through an inorganic film or a glassy film
consisting mainly of MgO and SiO.sub.2 which is formed on the
surface of the steel sheet in the course of the final annealing for
obtaining a secondary recrystallization. The fine strains can be
imparted to a steel sheet, for example, bringing a spherical
roller, or a body of rotation, having a small diameter of 10 mm or
less in contact with the steel sheet and rotatably moving it on the
steel sheet while the roller is weighted down with a slight load.
Of course, if the linear strains having the width of 600 .mu.m or
less can be given to the steel sheet without injuring the steel
sheet, any means can be employed to impart the linear strains to
the steel sheet.
FIG. 1 (a) is a microphotograph of the fine strain which is the
first feature of this invention. FIG. 1 (b) is a microphotograph of
the flaw given to a steel sheet, by the sharp edge of a knife which
is one of the prior means. As is noted from FIG. 1 (b), the flaw
forms a groove on the base steel and return strains are caused on
both sides of the groove. On the other hand, the fine strains of
this invention are considerably fine as if the base steel was not
deformed at all. The deformation only forms a slightly concave
hollow or recess which can microscopically be observed. Thus, the
strains of this invention are fine but, when the steel sheet to
which the strains are given and the glassy coating of which are
thereafter peeled off is observed by a transition pit method, it
can be found that the points showing the existence of the
transition form two rows of parallel lines at the distance or space
of 50 .mu.m so, as shown in FIG. 2 (a).
On the other hand, when the linear flaw formed by the knife is
observed, it can be found that a large number of oblique sliding
lines are formed with a high density since the amount of
deformation is large, as shown in FIG. 2 (b). The occurrence of the
sliding lines means that a strong shear is imparted to the steel
sheet. As mentioned above, however, the fine strains of this
invention are much smaller in amount of plastic deformation than
the flaws provided by the knife and the former is quite different
in shape from the latter. In the FIG. 2 (b) 1 is return strain
which means the strains accumulated at both the sides of the
groove.
FIG. 2 (c) shows an enlarged sectional view of FIG. 2 (a). As is
noted from FIG. 2 (c), the glassy film of the steel sheet is not
teared off, that is, the portion of the steel sheet provided with
the fine strain is coated with the glassy film, and, therefore,
even if the steel sheets are stacked, or piled, the current loss is
not caused, as shown in FIG. 2 (e).
On the other hand, as is shown in FIG. 2 (d) which is an enlarged
sectional view of FIG. 2 (b), the glassy film of the steel sheet is
teared off at the flaw or groove portion. Consequently, when the
steel sheets provided with the flaws are stacked, or piled, the
currents are discharged from the grooves whereby the current loss
is increased, as shown in FIG. 2 (f). In the above FIGS. 2 (c) to 2
(f) 2 is a base steel sheet and 3 is a glassy film.
One example of the methods for giving the fine strains of this
invention to a steel sheet is described in detail below.
The feature of the method is to rotatably moving a small spherical
roller made of a hard material and having its slightly convex
contact surface on a steel sheet to be provided with fine strains
while the roller is weighted down with a slight load.
The fine strains can be given to the base steel without injuring
the surface of the steel sheet including its glassy film by this
method since the small roller having the slightly convex surface is
rolled on the surface of the steel sheet while the roller is
weighted down with the slight load, as stated above. It is
preferable that the diameter of the roller is between 0.2 and/0 mm.
The width of the linear strain imparted by the roller having such a
width is between 10 and 600 .mu.m, preferable 300 .mu.m or less. It
is, however, undesirable to use a roller having its width larger
than the above range since the inner region defined by the parallel
lines shown in FIG. 2 (a) becomes too broad. To the contrary, in
case that the diameter of the roller ball is smaller than the above
range, it becomes easy to injure the surface of the steel sheet and
the glassy film. The depth of the slightly concave hollow formed by
the provision of the linear strain of this invention is 5 .mu.m or
less, ordinarily 1 .mu.m or so. If the depth of the concave hollow
exceeds 5 .mu.m, the flux density is greatly deteriorated and the
shape of the hollow becomes bad.
The above is only one example of the methods for giving the fine
strains to a steel sheet. As another method, for example, a small
disc having the large thickness and having the concave contact
surface traverse to the moving direction may rotatably be moved on
the surface of the steel sheet while the disc is weighted down with
a load. In addition, the above-stated roller, disc or a ball may be
slid on the steel sheet without injuring it.
In order to reduce the iron loss it is preferable that the strains
are given to the steel sheet in such an amount that the two row of
parallel lines can be observed as transition pits. The strains
exceeding the amount partially causes the great roughness on the
surface of the steel sheet whereby it is prevented to obtain an
expected magnetism or the space factor is deteriorated.
Furthermore, the strains may be given either to both side surfaces
of the steel sheet or to only one side surface.
Thus, one of the features of this invention is to give the fine
strains to the surface of the base steel of the steel sheet. In
addition, the steel sheet provided with the fine strains may have a
glassy film or a secondary coating thereon, as described later. Of
course, the fine strains can be given directly to a steel sheet
which does not have such a coating or film.
The reasons why it is preferable to give the strains to the base
steel sheet through the glassy film which is the second one of the
features of this invention are described below.
The glassy film is mainly made of the MgO applied prior to a final
annealing and the Si contained in the steel sheet. The film acts
not only to prevent the occurrence of the curing during the final
annealing but also to give a tension to the surface of the steel
sheet so as to decrease the iron losses. However, the removal of
the glassy film requires the use of such a strong acid as a fluoric
acid or a hydrochloric acid and a long time pickling which means
the addition of one step in an industrial treating line. Besides,
the magnetism of the steel sheet is deteriorated by the
disappearance of the tension effect and the surface roughness of
the steel sheet due to the pickling. Such disadvantages offset the
effects obtained by giving the fine strains to the steel sheet.
In the prior method of using a knife, the surface flaws have been
given directly to the base steel of the steel sheet. Therefore, it
is found that the prior method is inferior in effect to this
invention, when the former is compared with the latter on the basis
of the magnetism before removal of the film, as shown in FIG. 3.
However, the fine strains of this invention can also be given
directly to the surface of the steel sheet without pickling, in
case that the steel sheet is finally annealed in a final annealing
step which does not require the use of such an annealing separating
agent is MgO, for example, in a continuous annealing furnace.
The direction of the line of the linear fine strain of this
invention is described in detail below.
FIG. 4 (a) is a graph showing the change of the iron loss (W17/50)
at the time when the fine strains are given to only one side
surface of a steel sheet through its glassy film in the direction
of the angle .alpha. to the rolling direction and, therewith, the
steel sheet is magnetized at the rolling direction (L
direction).
In .alpha.<10.degree. the iron loss is rather deteriorated but
it is decreased as the .alpha. is increased. In
.alpha..gtoreq.30.degree. the iron loss is 5% or more and in
.alpha..gtoreq.45.degree. it shows the rate of improvement of 10%
or more. Accordingly, in order to greatly improve the iron loss the
angle .alpha. should be made 30.degree. or more, preferably
40.degree. or more. In case that the steel sheet is employed as a
core for coiled iron core, only the iron loss of the L direction
may be taken into account, but it becomes important to take account
of the iron loss at the time when the steel sheet is magnetized in
the direction (C direction) right-angled to the rolling direction,
namely the iron loss of the C direction, in dependence on the use
of the steel sheet.
The iron loss of the C direction can be improved by decreasing the
angle .alpha. in contrast with the iron loss of the L direction. As
is understood from FIG. 4 (b), for example, it is preferable that
the line of the fine strain is provided in the direction that the
angle .alpha. meets the range between +.degree. and 80.degree. from
the viewpoint of the improvement of the magnetism of both the L and
C directions. In addition, the line is not always a straight line
but it may be a curved line, a zig-zag line or a waved line.
Moreover, the lines may intersect on the steel sheet.
A preferable distance, or space, between the adjacent two fine
strains is stated below.
FIG. 5 is a graph showing the relation between the iron loss and
the distance between the adjacent two fine strains in case that the
roller having the diameter of 0.7 mm with a load of 200 g is
rotatably moved on the glassy film having the thickness of about 1
.mu.m in the C direction. From FIG. 5 it is noted that the optimum
distance is 2.5 to 10 mm. The value of the iron loss approaches the
value before the providing of the fine strains the more nearly, the
shorter the distance becomes. When the distance becomes 0.6 mm, the
iron loss becomes the same value as that before the impartment of
the fine strains.
In the same manner as the above the magnetic flux density (B8) is
deteriorated the more remarkably, the shorter the distance becomes.
It is noted from FIG. 5 that, when the distance is made from 2.5 mm
to 1.25 mm the flux density is deteriorated in an amount of about
0.01 (T) and when the distance is made from 1.25 mm to 0.6 mm, the
density is deteriorated in an amount of about 0.02 (T). In this
connection, the example in which the flaws having the depth of 10
.mu.m are given to the same steel sheet at the distance of 0.6 mm
in the C direction by a needle having a sharp tip end is shown by a
mark O in FIG. 5. From the example it is understood that both the
iron loss (1.25 W/Kg) and the B8 are rapidly deteriorated from the
values before the provision of the flaws and the provision of large
strains at small distance has rather bad influences on the steel
sheet.
Of course, the optimum distance is changed depending upon the
weight of the load imparted. As is shown in FIGS. 6 (a), (b) and
(c), for example, in case that the roller has the diameter of 0.7
mm, the optimum distance is made large as the weight of the load is
increased. Furthermore, as is understood from FIGS. 7 (a) and (b),
the magnetism is also fluctuated depending upon the change of the
width of the strain itself. That is, when the distance is 5 mm and
the width is 250 .mu.m, the iron loss becomes the same value as
that before the impartment of the fine strains and, when the
distance is 10 mm and the width is 400 .mu.mm, the iron loss
returns back to the same value. In addition, in case that the
distance is 15 mm and the width is 600 .mu.m, the iron loss becomes
the same value as that before the impartment of the fine strains.
In the same manner as the above, the B8 is reduced in an amount of
about 0.01 (T) in the respective 250 .mu.m, 400 .mu.m and 600
.mu.m. Accordingly, the width of the fine strain itself should be
made 600 .mu.m or less, preferably 300 .mu.m or less. It is, thus,
understood from FIGS. 5 to 7 (b) that the optimum distance between
the adjacent two strains and the optimum wide of the fine strain
should be determined, case by case, considering the weight of the
load to be imparted, how to give the fine strains to the steel
sheet and the thickness of the glassy film but that they should not
be made less than 2.5 mm and more than 600 .mu.m. In FIGS. 7 (a)
and (b) the fine strains are given to a steel sheet by the use of a
roller having the diameter of 0.7 mm and the width of the strain is
broadened by rotatably moving the roller on the steel sheet
repeately.
On the other hand, in the prior method using a knife which leaves
flaws the preferable distance is between 0.1 and 1 mm. Therefore,
in this invention the fine strains can be given to the steel sheet
with less density than that in the prior method whereby the time
and labor for giving the fine strains to the steel sheet can
greatly be reduced. In addition, the deterioration of the
excitation characteristics (B8) caused by the provision of the
flaws is as much as 0.02 T or so in the prior method but in this
invention the deterioration can be reduced to the minimum, i.e.
0.01 T or less. In this respect, the B8 shows the magnetic flux
density in 800 A/m.
It is preferable to put a steel sheet or steel strip in the
condition that a tension is preliminarily imparted thereto, in case
that the impartment of the fine strains is made in a continuous
treating line, since the tension acts not only to bear the load
necessary to give the strain to the steel sheet but also to further
promote the effect obtained by the impartment of the strain.
The glassy film formed in the final annealing has the thickness of
1 to 3 .mu.m and the thickness of such a degree is optimum to give
the fine strains to the steel sheet. However, when the thickness of
the glassy film is 5 .mu.m or less, the fine strains can be given
to the steel sheet without injuring the film.
The coating solution or agent to be applied for forming the glassy
film prior to the final annealing consists mainly of MgO, and
TiO.sub.2, the compounds of boron, sulfides or the compounds of
antimony may be added thereto in order to improve the adhesion or
magnetism of the film.
When this invention is applied to an electromagnetic steel sheet
having such a high magnetic flux density that B8 is 1.90 To or
more, the effect of this invention is further enhanced. FIG. 8 is a
graph showing the relation between the B8 and the values of the
iron loss (W17/50) before and after fine strains are imparted to a
steel sheet having the thickness of 0.30 mm. The increase of the B8
before the impartment of the fine strains reduces the iron loss but
the grade of the reduction becomes loose gradually as the B8
increases. When B8>1.93 T, the iron loss appears to approach the
saturation point. On the other hand, the iron loss after the
impartment of the fine strains is changed, or decreased, more
rapidly than the iron loss before the impartment in accordance with
the increase of the B8, that is the absolute value of the grade of
the reduction is larger than that before the impartment. In
addition, the iron loss is reduced down to a high B8, i.e. 1.95 T,
and it does not show the saturation tendency. Accordingly, it is
understood from FIG. 8 that the effect obtained by the impartment
of the fine strains becomes the more marvelously, the higher the B8
becomes. In the prior method the increase of the B8 has not been
sufficiently reflected upon the improvement of the iron loss but in
this invention it has been made possible to reflect the enhancement
of the B8 directly upon the decrease of the iron loss. In this
invention, thus, the marvelous low values of the iron loss have
been obtained as follows:
If B8.gtoreq.1.90 T, W17/50.ltorsim.1.03 W/Kg;
if B8.gtoreq.1.92 T, W17/50.ltorsim.0.96 W/Kg; and
if B8.gtoreq.1.94 T, W17/50.ltorsim.0.90 W/Kg:
In case that a material showing such a very low iron loss that the
W17/50 is 0.90 W/Kg or less is used in such an electrical equipment
as a transformer, it reduces power loss in an amount of 10% or
more, as compared with the power loss of the material having a low
iron loss which is used in an conventional equipment of the highest
grade. Therefore, the effect of this invention is immeasurable at
the present time when the saving of energy is required
worldwidely.
The step for the impartment of the fine strains of this invention
may be put into any position after the secondary recrystallization
is completed. For example, the step may be provided right after the
final annealing step or it may be positioned after the heat
flattening step. In case of a continuous final annealing line, the
step for the impartment of the fine strains can be placed in the
course of cooling. However, the fine strains should be given to a
steel sheet at a temperature of 800.degree. C. or less, preferably
700.degree. C. or less.
The steel sheet provided with the fine strains as it is can be made
a final product, but in general it is coated with the compounts of
phosphoric acid system or of organic system as a secondary coating
so that the insulation of the steel sheet is improved and
thereafter the steel sheet is made a final product. The secondary
coating should be carried out at a temperature of 800.degree. C. or
less, preferably 700.degree. C. or less. In the case, an
ultraviolet ray-hardening resin can be employed as the secondary
coating material instead of the above compounds.
In case that the steel sheet is provided with the fine strains
after the secondary coating is formed thereon or after the steel
sheet with the secondary coating is punched out, it is important to
take the following matter into consideration. That is, the case
that the fine strains are imparted to the steel sheet through the
secondary coating requires heavier load than the case that the fine
strains are given to the steel sheet through only the glassy film.
Therefore, the fine strains must be imparted to the steel sheet so
as not to injure the secondary coating. Of course, when the
secondary coating formed is a thin and strong one, it is possible
to decrease the iron loss without injuring the insulation even if
the fine strains are imparted to the steel sheet through the
secondary coating.
The shape of the roller, or a body of rotation, suitable for giving
the linear fine strains to a steel sheet is explained below.
One typical example of the preferable shapes of the roller is shown
in FIGS. 9 (a) and (b). As is noted from FIGS. 9 (a) and (b) the
surface of the roller contacting with the surface of the steel
sheet to be provided with the fine strains is made slightly convex
in order to provide the base steel with the fine strains of a
slightly concave hollow without injuring the glassy film or the
secondary coating. Therefore, it is not that the roller to be
employed for this invention is limited to the shape of the typical
example but that any shapes of rollers can be employed if their
surfaces contacting with the surface of the steel sheet are made
slightly convex, in the direction traverse to the moving
direction.
In addition, the lower iron loss can be obtained by the providing
of the fine strains, the higher the B8 of the steel sheet is or the
lower the iron loss of the steel sheet before providing the fine
strains is. Therefore, the effect of this invention can be enhanced
by finishing the steel sheet subjected to a final annealing to a
mirror or speculum condition before the steel sheet is provided
with the fine strains.
Examples of this invention are described below.
EXAMPLE 1
A steel ingot composed of 0.051% C, 2.95% Si, 0.083% Mn, 0.01% P,
0.025% S, 0.027% Al, 0.0076% N, the rest Fe and a very small amount
of unavoidable impurities is subjected to a series of a hot
rolling, an annealing, a rapid cooling, a cold rolling, a
decarburization annealing, a MgO coating and a final annealing in
order whereby a secondary recrystallization is completed. The grain
oriented silicon steel sheet thus produced has the thickness of
0.30 mm and is coated with a glassy film having the thickness of
1.5 .mu.m. Linear fine strains are imparted to one side surface of
the steel sheet by rotatbly moving a roller having the diameter of
0.7 mm straightly on the steel sheet at the space of 10 mm in the C
direction while the roller is weighted down with 200 g load. The
magnetisms of the rolling direction of the steel sheet before and
after the impartment of the fine strain are as follows:
Before the impartment; when B8=1.930 T, W17/50=1.10 W/Kg.
After the impartment; when B8=1.927 T, W17/50=0.97 W/Kg.
As is noted from the Example, the iron loss is greatly improved in
this invention.
EXAMPLE 2
A steel ingot composed of 0.048% C, 2.93% Si, 0.085% Mn, 0.008% P,
0.026% S, 0.025% Al, 0.0072% N, the rest Fe and a very small amount
of unavoidable impurities is subjected to a series of a hot
rolling, an annealing, a cold rolling, a decarburization annealing,
a MgO coating and a final annealing in order whereby a secondary
recrystallization is completed. The grain oriented silicon steel
sheet thus produced has the thickness of 0.30 mm and is coated with
a glassy film. The steel sheet is further subjected to a heat
flattening treatment and, thereafter, linear fine strains are
imparted to one side surface of the steel sheet by rotatably moving
a roller having the diameter of 0.5 mm straightly on the steel
sheet at the space of 8 mm in the C direction while the roller is
weighted down with 150 g load.
The magnetisms of the rolling direction of the steel sheet before
and after the impartment of the strains are as follows:
Before the impartment; when B8=1.950 T, W17/50=1.02 W/Kg.
After the impartment; when B8=1.948 T, W17/50=0.89 W/Kg.
In addition, the space factor, or stacking factor, measured in
accordance with the method defined in Japan Industrial Standard is
97%. On the other hand, the same steel sheet with the glassy film
is provided with linear flaws at the same space by the sharp edge
of a knife. In the case the space factor is 95%.
EXAMPLE 3
A steel ingot composed of 0.045% C, 3.05% Si, 0.040% Mn, 0.005% P,
0.006% S, 0.089% Sb, 0.030% Se, the rest Fe and a very small amount
of unavoidable impurities is subjected to a series of a hot
rolling, an annealing, a cold rolling, a decarburization annealing,
a MgO coating and a final annealing in order whereby a secondary
recrystallization is completed. The grain oriented silicon steel
sheet thus produced has the thickness of 0.35 mm and is coated with
a glassy film. Linear fine strains are given to both side surfaces
of the steel sheet by straightly sliding a roller having the
diameter of 1 mm on the steel sheet at the space of 10 mm in the
direction of 35.degree. to the C direction while the roller is
weighted down with 300 g load. The magnetisms of the steel sheet
before and after the impartment of the strains are as follows:
Before the impartment:
L direction; when B8=1.95 T, W17/50=1.17 W/Kg;
C direction; when B8=1.35 T, W13/50=2.92 W/Kg.
After the impartment:
L direction; when B8=1.95 T, W17/50=0.99 W/Kg;
C direction; when B8=1.34 T, W13/50=2.22 W/Kg.
EXAMPLE 4
A steel ingot composed of 0.049% C, 2.95% Si, 0.080% Mn, 0.025% S,
0.028% Al, 0.0070% N, the rest Fe and a very small amount of
unavoidable impurities is subjected to a series of a hot rolling,
an annealing, a cold rolling, a decarburization annealing and a
final annealing in order whereby a secondary recrystallization is
completed. The grain oriented silicon steel sheet thus produced is
further coated with the solution containing phosphoric acid and
chromic acid as main components and thereafter is cured at the
temperature of 800.degree. C. to produce a secondary coating
thereon. Linear fine strains are imparted to one side surface of
the steel sheet with the secondary coating by rotatably moving two
rollers having the diameters of 1 mm and 10 mm on the steel sheet
at the space of 5 mm in the direction right angled to the rolling
direction. The magnetisms of the steel sheet before and after the
impartment of the strains are as follows:
______________________________________ B.sub.8 (T) W 17/50 (W/Kg)
______________________________________ A Before the impartment
1.940 1.03 After the impartment 1.938 0.92 (diameter: 1 mm) B
Before the impartment: 1.938 1.03 After the impartment (diameter:
10 mm) 1.934 0.94 ______________________________________ Remarks A
transition pit method (electrolytic corrosion) electrolytic
solution: chromic anhydride 50 g glacial acetic acid 130 cc water
180 cc current density: about 3A/cm.sup.2 Corrosion time: about 2
minutes washing: 30% hydrochloric acid
______________________________________
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